(1.) Field of the Invention
The present invention relates to a process for producing polyester fibers having excellent tensile properties.
The polyester fibers produced by the present invention are suitable for use as industrial materials, particularly as reinforcement materials for tire, belts, etc.
(2.) Description of the Prior Art
It is known from Kobunshi Ronbunshu (vol. 42, pp. 159-166, 1985) that highly oriented low specific gravity polyester fibers can be obtained by drawing at a temperature lower than the glass transition temperature of the polyester.
It is also known, according to Japanese Patent Kokai (Laid-open) No. 169513/83, that in the production of high-speed spun amorphous polyethylene terephthalate yarns for producing textured yarns, the extruded filaments are quenched in a liquid bath placed under the spinneret.
According to Japanese Patent Kokai (Laid-open) No. 210590/83, it is also known that highly oriented low specific gravity polyester filaments can be obtained by stretching, using laser beams, and that highly oriented low specific gravity polyester filaments can be improved in tensile properties by heat treatment of the filaments.
The above mentioned process, employing conventional techniques, has some disadvantages in terms of productivity, property and installing expense.
For example, in the case of the process mentioned in Kobunshi Ronbunshu, 42, 159, 1985, highly, oriented low specific gravity polyester fibers, drawn at lower temperatures than glass transition temperatures should be spun at lower speed than one in which orientation induce crystallization occurs, and required a huge drawing apparatus for industrial production. This means low productivity and high installing expense. Also the tensile property of yarn by this method is not sufficient for industrial use.
In the case of Japanese Patent Kokai (Laid-open) No. 169513/83, this method relates to a method of producing textured yarns which has high shrinkage properties. Inevitably, the tensile properties are not enough for industrial use, and also the winding speed is higher than 5000 m/min; this means very high facility expenses.
In the case of Japanese Patent Kokai (Laid-open) No. 210590/83, this process uses laser power for drawing to obtain highly oriented low specific gravity polyester filaments. The apparatus used in such process, however, requires high power and is huge, expensive and dangerous in operation. Also, according to such a process, further heat treatment is required to obtain low shrinkage properties for industrial use.